The cDNA encoding IL-11 was isolated from a primate bone marrow stromal cell line through mammalian cell expression cloning method based on its ability to stimulate the proliferation of an IL-6-dependent mouse plasmacytoma cell line, T1165. Like most of the cytokines, IL-11 exerts various biological activities through the interactions-between the ligand and the receptors present on the target cells. IL-11 has been shown to be able to synergize with IL-3 in supporting human and murine megakaryocyte colony formation, stimulate the T-cell dependent development of immunoglobulin-producing B cells and act synergistically with IL-3 to shorten the Go period of early hematopoietic progenitors. Recent studies have shown that IL-11 can also induce the synthesis of acute-phase proteins and inhibits the process of adipocyte differentiation. The fact that an adipocyte cell line, 3T3-Ll, can respond to a stromal fibroblast-derived growth factor like IL-11, may .provide a useful system to study the cell-cell interactions in the hematopoietic microenvironment. The long term objective of this proposal is to understand the role of IL-11 in regulating hematopoiesis at the molecular and cellular level. Since most of the biological activities of IL-11 overlaps with those of IL-6, we hypothesize that these two cytokines may utilize similar signal transduction pathways or may even share common receptors. The proposed work aims to (1) molecularly clone the IL-11 receptor: this will be achieved by (i) cloning the receptor based on the functional interaction between the i ligand and the receptor by screening a 3T3-Ll cDNA expression library based on the ability of the IL-11 receptor cDNA expressing IL-3-dependent FDCP-1 cells to grow in the presence of IL-11 and in the absence of IL-3; (ii) cloning the receptor based on the ligand binding by screening a 3T3-Ll cDNA expression library using microscopic emulsion autoradiography with radioiodinated IL-11 and (2) study IL-11-mediated signal transduction pathways in comparison with those of IL-6: this will be accomplished by (i) analyzing the significance of protein tyrosine phosphorylation, G protein, protein kinase C and adenyl cyclase in IL11-mediated sinal transduction pathways; (ii) identifying phospholipid-derived second messengers involved in the IL-11-mediated signaling; (iii) examining the primary response genes activated by IL-11-mediated signal transduction. The accomplishment of this proposal will not only help us better understand the biological relevance of IL-11 and cell-cell interactions in the normal hematopoietic microenvironment but also uncover some of the mechanisms involved in the IL-11-mediated signal transduction.